Add some useful elabinelab sitevars.

New sitevars:
elabinelab/singlenet set the system-wide default for cnet implementation
elabinelab/boss_osid default OSID for boss node
elabinelab/ops_osid default OSID for ops node
elabinelab/fs_osid default OSID for fs node
Also mark the various elabinelab/*pkg* sitevars as deprecated. Package
versions are just too dependent on the OS running and we almost always
wind up overriding these sitevars in rc.mkelab anyway.